This invention relates generally to prefabricated concrete floor or roof panels with embedded composite steel joists or trusses and methods for making same. More particularly, the invention relates to such assemblies where the embedded joists consist of a bottom chord and a zig-zag web member, the web member being embedded directly in the concrete. Even more particularly, the invention relates to such assemblies where the concrete is cast into a cambered mold with the joist correspondingly cambered, such that when the concrete panel has hardened, is removed from the mold and inverted, the weight of the panel together with the creep of the concrete during final curing will diminish or eliminate the camber to produce a generally flat roof or floor member.
Concrete floors or roofs are commonly used in building construction, the floors or roofs being poured on site on forms built onto joists or trusses. This is a relatively slow and labor intensive method of constructing these floors and roofs. Concepts of modular construction can be utilized in the construction of concrete floors or roofs, the floors or roofs being formed of precast concrete panel and composite joist assemblies which are set into place in the building and joined together to create a unified floor or roof. Previous efforts at manufacturing these precast assemblies have encountered numerous problems, most of which stem from the fact that the known methods utilize flat molds which produce flat concrete panels with joists connected to one side of the panel. Because the panels have significant weight and due to the shrinkage of the concrete during final curing, they will flex in the center when installed so that the floor or roof has a negative camber rather than being flat or planar.
It is an object of this invention to provide a method of producing a precast concrete panel and composite joist assembly which can be used to create floors, roofs or the like, the method being an improvement over known precast techniques with regard to economy of time and money, as well as in producing a superior assembly. It is a further object to provide such a method which results in precast concrete panel and composite joist assembly which has a residual positive camber to counter the weight and curing creep effects inherent in the panel. It is a further object to provide such a method which utilizes a casting table or mold having a camber, as well as joists having corresponding cambers, where the mold can be used to form multiple panels simultaneously.